#include <stdio.h>
#include <stdlib.h>
#include <string.h> 

#define MAX_SIZE 12 

char *strcat_1(char a[], char b[]);

char x[MAX_SIZE] = {'H', 'e', 'l', 'l', 'o', '\0'};
char y[] = {'W', 'o', 'r', 'l', 'd', '\0'};

int main()
{
    char *result = strcat_1(x, y);
    printf("%s\n", result);
    system("pause");
    return 0;
}

char *strcat_1(char a[], char b[])
{
    int i = 0;
    while (b[i] != '\0')
    {
        a[strlen(a)] = b[i];
        i++;
    }
    a[strlen(a)] = '\0'; 
    return a;
}
